Basicity catalytic performance

This chapter compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It is proposed that with the basic catalyst, Mg/Fe/0, the tme alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacts with phenol to yield salicyl alcohol, which rapidly dehydrogenates to salicyladehyde. The latter was isolated in tests made by feeding directly a formalin/phenol aqueous solution. Salicylaldehyde then transforms to o-cresol, the main product of the basic-catalyzed methylation of phenol, likely by means of an intramolecular H-transfer with formaldehyde. With an acid catalyst, H-mordenite, the main products were anisole and cresols moreover, methanol was transformed to alkylaromatics. 

The effect of temperature on the catalytic performance of Mg/Fe/O is reported in Figure 3. The behavior was quite different from that of the Mg/Al/O catalyst. The conversion of m-cresol with Mg/Fe/O was always lower than that with Mg/Al/O. The selectivity to 3-MA was almost negligible in the whole range of temperature. The selectivity to polyalkylates and to 3,4-DMP was also much lower than that observed with Mg/Al/O. Therefore, the catalyst was very selective to the products of ortho-C-methylation, 2,3-DMP and in particular 2,5-DMP. This behavior has to be attributed to specific surface features of Mg/Fe/O catalyst, that favor the ortho-C-methylation with respect to O-methylation. A different behavior of Mg/Al/O and Mg/Fe/O catalysts, having Mg/Me atomic ratio equal to 4, has also been recently reported by other authors for the reaction of phenol and o-cresol methylation [5], The effect was attributed to the different basic strength of catalysts. This explanation does not hold in our case, since a similar distribution of basic strength was obtained for Mg/Al/O and Mg/Fe/O catalysts [4],... 

Fontes tt al. [224,225 addressed the acid—base effects of the zeolites on enzymes in nonaqueous media by looking at how these materials affected the catalytic activity of cross-linked subtilisin microcrystals in supercritical fluids (C02, ethane) and in polar and nonpolar organic solvents (acetonitrile, hexane) at controlled water activity (aw). They were interested in how immobilization of subtilisin on zeolite could affected its ionization state and hence their catalytic performances. Transesterification activity of substilisin supported on NaA zeolite is improved up to 10-fold and 100-fold when performed under low aw values in supercritical-C02 and supercritical-ethane respectively. The increase is also observed when increasing the amount of zeolite due not only to a dehydrating effect but also to a cation exchange process between the surface proton of the enzyme and the sodium ions of the zeolite. The resulting basic form of the enzyme enhances the catalytic activity. In organic solvent the activity was even more enhanced than in sc-hexane, 10-fold and 20-fold for acetonitrile and hexane, respectively, probably due to a difference in the solubility of the acid byproduct. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

In summary, the basicity and the strong NiO-MgO interactions in binary NiO/MgO solid solution catalysts, which inhibit carbon deposition and catalyst sintering, result in an excellent catalytic performance for C02 reforming. The characteristics of MgO play an important role in the performance of a highly efficient NiO/MgO solid-solution catalyst. Moreover, the NiO/MgO catalyst performance is sensitive to the NiO content a too-small amount of NiO in the solid solution leads to a low activity, and a too-high amount of NiO to a low stability. CoO/MgO solid solutions have catalytic performances similar to those of NiO/MgO solid solutions, but require higher reaction temperatures. So far, no experimental information is available regarding the use of a FeO/MgO solid solution for CH4 conversion to synthesis gas. 

The most active catalysts for NH3 decomposition are based on Ru, however, cheaper Fe, Co, Ni and alloy systems are also intensely investigated [148]. The impact of the support material is remarkable. In a study by Au et al., Ru/CNTs performed better than all oxide-supported systems, whereas activated carbon resulted in one of the lowest NH3 conversions (Tab. 15.6) [147]. The dispersion of the active component as well as basicity [147] and conductivity [149] of the support are discussed as the relevant factors for high catalytic efficiency. However, the difference between CNT and activated carbon support is still remarkable. Thus it is not surprising that even the residual catalyst material on commercial MWCNTs, which is basically based on Fe and Co, results is a high catalytic performance in NH3 decomposition [150]. 

Introduction of zeolites into catalytic cracking improved the quality of the product and the efficiency of the process. It was estimated that this modification in catalyst composition in the United States alone saved over 200 million barrels of crude oil in 1977. The use of bimetallic catalysts in reforming of naphthas, a basic process for the production of high-octane gasoline and petrochemicals, resulted in great improvement in the catalytic performance of the process, and in considerable extension of catalyst life. New catalytic approaches to the development of synthetic fuels are being unveiled. 

Figure 9. A comparison between the catalytic performance through 2,6-xylenol yield, and relative acidity (solid diamonds) obtained from the area of v8a and vl9b bands from pyridine adsorbed on catalyst surface at lOOOC and the relative basicity (solid circles) obtained from the area of the bands between 1700 and 1250 cm-1 from C02 adsorbed on Cul-xCoxFe204 catalysts at 250C.

The AlGaPON samples were used as catalysts of the Knoevenagel condensation reaction and the authors [211] found that the -NH2 groups present at the surface of the samples were the basic sites responsible for the condensation properties of the catalysts. The catalytic performances of the studied samples increased with their basic character observed by SO2 adsorption microcalorimetry. 

The use of the upper rim of calix 4 arcncs, blocked in the cone conformation, as convenient platforms for the introduction of metal ion binding sites is well documented [26e,291. Table 5.9 shows the catalytic performances of regioisomeric vicinal 21-Ba2 and distal 22-Ba2, and of the m-xylylene derivative 17-Ba2 in the basic ethanolysis of esters 14 and 23-25 [30]. 

In view of what precedes, it has been the aim of the present work to identify the Ru-species present in faujasite-type zeolites activated under WGS-conditions, making use of the avail-albe literature data. The activation procedure of Ru(III)hex-ammine in NaY has been related to its catalytic performance as low temperature WGS-catalvst. Subsequently, the basicity of the material was related to its catalytic behavior in the same reaction, by changing the nature of the parent complex, of the charge compensating cations and of the aluminum content of the faujasite-type zeolite. 

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